Hardest: Gridion!!!
It requires 3 teams (Offense, Defense and Special Teams to have a complete meltdown to lose to a shitty side)

Easiest: Pornography.

In my sporting arena, i am known as upset king... the director says we need a good cunshot but i end up upsetting all over her chest and she hasn't even had time to take her clothes off and allow me to work my magic.

In my sporting arena, i am known as upset king... the director says we need a good cunshot but i end up upsetting all over her chest and she hasn't even had time to take her clothes off and allow me to work my magic.

Either way it is baseball just because a pitcher can go off on any single game and shut down a team. Hockey is up there just because goalies can get hot. Same can be sai for soccer.

Basketball is probably the most difficult. Tennis is pretty hard as well. The more points/chances in a given match the harder it is to pull an upset because the better team has more chances to exhibit their dominance.